1. Field of the Invention
This invention relates generally to methods and apparatus for monitoring subjects afflicted with various diseases, and specifically to the non-invasive monitoring of physiologic parameters of a subject in the home environment, and communication of this information to a remote location such as a hospital or other medical facility.
2. Description of Related Technology
Congestive heart failure (CHF) is a common, but serious medical condition, which affects hundreds of thousands of people annually. The condition is caused by failure of the heart to function efficiently. In effect, the heart is unable to adequately pump blood throughout the body, which results in a general weakness and lethargy, especially when an individual attempts to exert themselves physically. The greater the severity of the disease, the less capable will be the individual to perform even routine daily activities such as walking, standing, and the like.
Unfortunately, after diagnosis of the condition, which is usually made with a series of tests including cardiac ultrasound, ECG and blood pressure readings, treatment is generally limited to pharmacological therapy including beta-blockers and diuretics to reduce the load on the heart. CHF patients who are otherwise in generally good health are often candidates for heart transplants.
For the majority of patients however, the major challenges are to learn how to alter their lifestyle and live in accordance with the disease limitations. Diet and limited exercise are often prescribed. In addition, a major emphasis is placed on prevention of weight gain, which is often associated with excessive fluid intake or failure to excrete sufficiently, both of which add load to the already failing heart. In many cases, dramatic and rapid changes can occur in an individual, including dyspnea, rapid heart rate and dizziness, if the ejection fraction of the heart falls below certain physiologic limits for a given individual. When this occurs, CHF patients are often emergent cases requiring hospital admission. Subsequently, the typical course of therapy for such patients is increased diuretic therapy to stabilize the situation and them return them to home care.
Medical practitioners generally agree that CHF patients can readily be maintained in their home environment providing that careful monitoring of the key cardiovascular components is routinely performed. Such routine monitoring may be required weekly, daily, or even hourly for certain subjects. Most importantly, the measurement of certain key parameters including weight change, heart rate, and blood pressure would allow for reasonable management of the subject in the home on a day-to-day basis. Changes in peripheral arterial oxygen saturation level, if known, would also be quite useful in the management of the subject. Other parameters relating to the subject""s physiology such as basic blood chemistry would also be of use if available. However, under the prior art, no apparatus or techniques exist which provide monitoring of the foregoing physiologic variables of a subject without extensive assistance from a clinician, spouse or other caregiver. Hence, the CHF patient is presently forced to choose between retaining a part- or full-time in-home caregiver, utilizing their spouse extensively (if one exists) as a caregiver, or routinely being transported to a medical facility or visited by a clinician/physician for monitoring. Each of these options has significant drawbacks, ranging from the cost of providing the required care in-home or at the designated medical facility, to the more intangible reduction in quality of life for both the subject and his/her spouse. Clearly, if a CHF (or other) subject could be routinely monitored at home without requiring any significant participation by a caregiver or his/her spouse, then significant benefits in terms of reduced healthcare costs and improved quality of life would be realized.
Another complicating factor in monitoring CHF patients relates to the measurement of blood pressure; routine blood pressure measurements such as those described above can be extraordinarily difficult because of technical limitations associated with current state-of-the-art xe2x80x9ccuffxe2x80x9d devices, such as those employing the well known auscultation or oscillometry techniques. Specifically, the accuracy of such existing cuff-based blood pressure monitoring devices may be greatly reduced in subjects having low blood pressures and very weak, xe2x80x9cthreadyxe2x80x9d (i.e., not steady, or firm) pulses. This reduced accuracy relates in great part to the method by which the cuff devices estimate blood pressure. Furthermore, even if good accuracy is achieved on certain measurements, the clinician or caregiver is left with substantial uncertainty as to which measurements obtained from the subject are accurate or reflective of the actual condition of the subject, and which are not.
Another intrinsic disability of existing blood pressure measurement techniques relates to their non-continuous nature. Specifically, prior art auscultation and oscillometry techniques are geared primarily to xe2x80x9cspotxe2x80x9d measurement of blood pressure; i.e., at one discrete point in time. As is well known in the medical arts, such spot measurements, even when accurate, may or may not be indicative of the actual physiologic state of the subject. For example, if the blood pressure of the subject is measured during an interval when their blood pressure is artificially increased or depressed, broader trends or patterns in the subject""s blood pressure may be masked. As with most any measurement process, observations made on the basis of few data points are generally less reliable and less meaningful than those made on the basis of many data points. In order to obtain a plurality of measurements using the aforementioned prior art techniques, the cuff would need to be inflated and deflated a number of different times, which is very cumbersome and uncomfortable for the subject. Furthermore, repeated inflations of a blood pressure cuff may cause nerve damage to the brachial plexus or damage to the underlying tissues. It is effectively impossible to obtain a truly continuous representation of a subject""s blood pressure using these prior art techniques, since there is a practical limit on how rapidly multiple consecutive measurements can be made. Errors due to respiration effects on blood pressure (due largely to the changing volume of the thoracic cavity) may also contribute to the inaccuracy of xe2x80x9cspotxe2x80x9d blood pressure measurements.
Continuous blood pressure measurements may be made using prior art invasive catheters (commonly known as xe2x80x9cA-linesxe2x80x9d), however, such devices require the actual surgical implantation of the catheter into the blood vessel of the subject, which is clearly not well suited to long-term daily monitoring of the subject""s blood pressure, especially in the home care environment.
In addition to the foregoing, it is often useful to compare values of other physiologic parameters measured concurrently with blood pressure in order to gain a broader perspective on the subject""s condition. Prior art blood pressure measurement techniques do not lend themselves well to such simultaneous monitoring, in large part due to the fact that they are xe2x80x9cspotxe2x80x9d measurements and not continuous in nature. Hence, unless the spot measurement is synchronized to coincide with the other measurements, simultaneous monitoring is not possible. In the context of home healthcare, it is unreasonable to expect a subject (or even a trained caregiver, for that matter) to obtain such synchronized measurements.
Hence, when considered as a whole, the use of cuff-based blood pressure measurement devices on CHF patients (or other subjects with low blood pressure and/or weak, thready pulses) generally produces results which are at best only snapshots of a subject""s true blood pressure, and at worst of questionable reliability and poor accuracy. Often, measurements of blood pressure taken by the subject using either automated or semi-automated techniques is questioned by professionals due to its suspected inaccuracy.
Based on the foregoing, what is needed is an improved method and apparatus for assessing a plurality physiologic parameters, including blood pressure, associated with a living subject. Such method and apparatus would ideally (i) be non-invasive, (ii) be integrated such that the monitoring of various parameters could be accomplished simultaneously (or near-simultaneously) and at one physical location so as to minimize discomfort and disturbance to the subject, and (iii) be both useful and produce reliable results under a variety of different subject physiological circumstances, such as for different subjects having a variety of different afflictions. Furthermore, such improved method and apparatus would be capable of monitoring a subject""s physiologic parameters in a desired location remote from a hospital or other medical facility (such as in the subject""s home), thereby obviating the need for both an in-home caregiver and routine visits by the subject to the hospital/medical facility.
The present invention satisfies the aforementioned needs by an improved method and apparatus for monitoring physiologic parameters, including blood pressure, within a living subject.
In a first aspect of the invention, an improved apparatus for monitoring a plurality of physiologic parameters of a living subject is disclosed. The apparatus generally comprises a monitoring station having means by which the blood pressure, electrocardiogram (ECG) and heart rate, and weight of the subject may be measured concurrently during a predetermined monitoring interval, and transmitted if desired to a remote location such as a medical facility for analysis or evaluation by a medical professional. In a first embodiment, the monitoring station comprises a support element, at least one ECG probe disposed relative to the support element, a blood pressure monitoring probe adapted for use on the radial artery of the subject, and a scale adapted to measure the weight of the subject while seated on the support element. The ECG probe comprises a pair of conductive handgrips which the subject grasps while seated; a pair of conductive footrests are also optionally provided to measure ECG data from the feet of the subject. The blood pressure monitoring probe is held within an assembly adapted to receive the wrist of the subject, providing access to the radial artery contained therein, when the subject grasps the handgrips. A continuous blood pressure monitoring apparatus is used to provide continuous blood pressure data for the subject during the monitoring interval. The monitoring station is also equipped with (i) a processor for processing data received from the ECG probe(s) and blood pressure probe, (ii) a display for displaying the data obtained during the monitoring interval, (iii) a storage device for storing data for later retrieval and analysis, and (iv) a communications link which allows data obtained from the subject to be transmitted to a remote location, as well as receiving data from the remote location. The monitoring station is also optionally outfitted with a pulse oximeter used to determine the relative percentage arterial oxygen saturation for the subject, and a blood chemistry probe used to perform certain rudimentary blood analyses on a sample of the subject""s blood obtained via a pin prick or other comparable technique. In a second embodiment, the monitoring station comprises a platform upon which the subject stands while the aforementioned parameters are monitored. In a third embodiment, the monitoring station is integrated with an exercise device to facilitate monitoring of the subject""s physiologic parameters during periods of exercise.
In a second aspect of the invention, an improved system for communicating medical information between a first location and a second, remote location is disclosed. The system generally comprises the aforementioned monitoring station disposed at the first location; a communications terminal (or plurality of terminals) disposed at the second location; and a communications link placing the monitoring station in data communication with the terminal. In a first exemplary embodiment, the communications terminal comprises a personal computer (PC) disposed in a medical facility such as a hospital, and the communications link comprises a pair of modulator/demodulator devices (modems) communicating across a public switched telephone network (PSTN). The modems may comprise digital subscriber line (DSL) modems which operate in conjunction with DSL-capable local loops on respective ends of the communications link to provide enhanced bandwidth. In a second embodiment, the communications terminal comprises a personal computer (PC) disposed in a medical facility such as a hospital, and the communications link comprises video conferencing link (such as that complying with ITU Standard H.323) implemented via a data network. Physiologic monitoring data obtained from the subject at the first location is transmitted to the remote communications terminal via the link and displayed on the terminal""s display screen for review by a caregiver; video and/or audio data is also optionally streamed from the monitoring station to the remote terminal (and vice versa) to allow face-to-face communications between the subject and the caregiver. Useful data, such as updated parametric data, analyses of monitored data, calibration data, and the like may also be transmitted from the caregiver to the monitoring station for display and use by the subject in real time. The monitoring station and terminal may also optionally be equipped with text-to-speech (TTS) and/or speech recognition capability to permit the subject and the caregiver to communicate in a variety of forms, such as by the caregiver typing a textual message into their terminal and having the message converted to audio instructions provided to the subject at their monitoring station, or alternatively, the subject providing a verbal report of their present condition, symptoms, etc., and having this report converted to text for inclusion in the data record of the subject reviewed by the caregiver. The operation of the monitoring station may be controlled by the subject using the aforementioned speech recognition system as well.
In a third aspect of the invention, an improved method of remotely monitoring a plurality of physiologic parameters within a living subject is disclosed. The method generally comprises measuring a first physiologic parameter from a blood vessel of the subject; measuring a second physiologic parameter from the subject; measuring a third physiologic parameter from the subject; comparing data derived from the measurements of the first, second, and third physiologic parameters to predetermined values of those parameters, respectively; and identifying when at least a portion of the data bears a predetermined relationship to at least one of the predetermined values. In one exemplary embodiment, the first parameter measured comprises blood pressure, the second heart rate (as derived from ECG measurement), and the third the weight of the subject. Predetermined values or ranges of values acceptable for the given subject are compared to the measurements obtained from the subject via the foregoing apparatus, and the relationship between the measured data and acceptable values/ranges identified.
In a fourth aspect of the invention, an improved method of providing treatment to a subject is disclosed. The method generally comprises the aforementioned method of monitoring the physiologic parameters of the subject, and further includes the steps of transmitting the results of the foregoing comparison to the caregiver at a remote location via a communication channel, analyzing the results at the remote location, and providing a course of treatment for the subject remotely via the communication channel.
In a fifth aspect of the invention, an improved computer program useful for monitoring the physiologic parameters of a subject and embodying the aforementioned methods is disclosed. In one exemplary embodiment, the computer program comprises an object code representation of a source code listing stored on the magnetic storage device of the aforementioned monitoring station, and adapted to run on the microprocessor thereof. In a second embodiment, the program comprises an assembly language/micro-coded instruction set disposed within the embedded storage device, i.e. program memory, of a digital signal processor (DSP) or microprocessor associated with the foregoing monitoring apparatus. In a third embodiment, the computer program comprises an object-oriented distributed application which comprises a plurality of client components distributed at a variety of subject locations, and a server component disposed on a server disposed at a central medical facility, whereby the client components interact and communicate with the server component via one or more data networks.
In a sixth aspect of the invention, an improved display for use in conjunction with the foregoing computer program and apparatus is disclosed. The display generally comprises a display architecture having a plurality of traces relating to respective ones of various physiologic parameters associated with a subject being remotely monitored. The parameters are displayed in temporal format (i.e., value of parameter versus time) for a predetermined monitoring duration, or continuously if desired. Optionally, the display is provided with videoconferencing and/or text messaging windows such that the subject (or conversely, the caregiver) can be viewed, and text messages exchanged, respectively. An analysis window is also provided whereby the results of special analyses performed by the monitoring station, caregiver""s communications terminal, or remote analysis equipment may be displayed for viewing by all parties on the network. For example, the monitoring station may be equipped with an algorithm for detecting arrhythmias present in the subject""s ECG data; the results of this arrhythmia analysis may be displayed in the aforementioned window. An icon-based touch screen menu structure allows the subject and/or caregiver to rapidly perform a predetermined set of monitoring analysis functions merely by touching the display screen in the appropriate location, including the retrieval of data stored either locally or remotely.